IPCC’s climate projections on target so far

Checking in on IPCC predictions going back to 1990.

The simplest way to evaluate a chef is to taste the food. So when thinking about climate science, the simplest way for the public to get a feel for the reliability of future projections is to see how past temperature projections have held up so far. A real evaluation of climate modeling would be (and is) much more involved and rigorous than that, but that’s a more challenging meal that most people have time for.

Many modeling studies result in projections about the future, but the consensus projections made in the Intergovernmental Panel on Climate Change reports are the highest profile. A pair of recent papers has gone back to those reports to see how well they match the trends we’ve observed since their release. It can take a couple of decades for climate trends to become clear, but the first IPCC report was published in 1990, so there’s now enough data to make a comparison worthwhile.

It’s been said that prediction is difficult—especially about the future. That’s certainly the case for climate, where unpredictable variability—from volcanoes, the El Niño Southern Oscillation, and subtle changes in solar output, for example—are collectively a large determinant of year-to-year changes. On top of that, trends in human emissions depend on unforeseeable socioeconomic circumstances. When IPCC reports project future changes, they don’t try to guess at these things. They project average trends for multiple scenarios of human emissions.

This means that the comparison between projections and observed temperatures is not quite as simple as it sounds. First, you’ve got to figure out how well the scenarios given in the reports match the actual amount of carbon dioxide we’ve emitted. Then, you’ve got to account for the natural year-to-year variability somehow. Only then can you have an apples-to-apples comparison.

The IPCC temperatures are on target

A paper in Nature Climate Change checks in on the projections from the first IPCC report, published in 1990. That report projected simple trends based on greenhouse gas emissions through 2030, a period we’re just over halfway through. The most frequently cited projection estimates 0.7–1.5°C of warming between 1990 and 2030, which means we would see an increase of about 0.35 – 0.75 °C through 2010. (The range of values is a product of uncertainty about the exact sensitivity of climate to greenhouse gases.) The observed temperature trend through 2010 is about 0.35–0.39°C, depending on the dataset.

So, is it as simple as saying the projection was (barely) correct, but overestimated warming? Not really. The first thing to do is account for natural variability. The researchers chose to address this by running many climate model simulations in a “stable” configuration with no drivers of warming or cooling. Ninety percent of the natural variability fell within a range of ±0.19°C. If you apply that as a measure of potential noise around the signal of the underlying trend, the projected warming by 2010 becomes 0.28 – 0.81°C, which includes the observed trend a little more cleanly.

It’s also important to note that both the projection and the observed trend lie above the estimated range of natural variability. That means the difference between the observed warming and natural variability is statistically significant.

There’s still the matter of emissions scenarios, though. That oft-cited 1990 projection is actually based on a higher level of emissions than we actually produced. The emissions scenario closest to reality gives a projected trend of 0.16–0.63°C through 2010 (using the researchers’ estimate for natural variability). The observed warming of 0.35–0.39°C is right in the middle of that range.

Our comparison might be down to apples and apples at this point, but it’s Granny Smith and Red Delicious. To really assess the IPCC projections, the researchers used a very simple climate model like the one used for that IPCC report and calibrated it to make sure it would yield the same results as the 1990 model. Then they fed in actual emissions data and added in the volcanic eruptions that have occurred, as well.

The result, including natural variability, was a predicted warming of 0.29–0.67°C by 2010. Twenty-two years ago, that’s where the report predicted we’d be at today.

Another paper, this one published in Environmental Research Letters (Open Access), takes a different approach. The researchers build on previous work in which they attempted to adjust global temperature data to remove most of the natural variability, dampening some noise and bringing out the signal. Comparing this data to the projections in the third and fourth IPCC reports (2001 and 2007) shows solid agreement.

Sea levels, less so

The researchers also compare the sea level projections associated with those reports to the observed sea level rise since their publication. Here the projections are less accurate. Sea level has very slightly exceeded the upper bound of the uncertainty range for the projections. The reports’ best estimate of projected sea level rise was about 2.0 millimeters per year—it has actually increased at a rate of 3.2 ±0.5 millimeters per year.

This isn’t a surprise, as the projections are considered to be conservative by many researchers. Uncertainty about how quickly Greenland and Antarctica will lose ice seems to be largely responsible for the cautious estimates. The researchers note that the difference between projected and observed sea level rise to this point (and what we know about ice sheets) “suggests that the 21st Century sea-level projections of the last two IPCC reports may be systematically biased low.”

The reality is that the IPCC projections have stood up well in some ways, and work is ongoing in others. This is the nature of scientific progress.

Each IPCC report is a summary of the science existing at the time. If there were no questions remaining or progress to make, climate scientists would have moved on to something more interesting. But underlying all the complicated details is a very simple relationship—adding greenhouse gases to the atmosphere raises temperatures and changes climate. That’s what the science predicted, and that’s what we’re seeing play out.

The DOI for the the ERL link isn't resolving right now, and I can't get the journal's web page to load just yet. But the Nature Climate Change paper sums the situation up nicely in the abstract:

David J. Frame & Dáithí A. Stone wrote:

In 1990, climate scientists from around the world wrote the First Assessment Report of the Intergovernmental Panel on Climate Change. It contained a prediction of the global mean temperature trend over the 1990–2030 period that, halfway through that period, seems accurate. This is all the more remarkable in hindsight, considering that a number of important external forcings were not included. So how did this success arise? In the end, the greenhouse-gas-induced warming is largely overwhelming the other forcings, which are only of secondary importance on the 20-year timescale.

All they are doing testing the old model by adjusting some parameters. It seems to be a good model after all

Actually, I was wondering about that.

Quote:

To really assess the IPCC projections, the researchers used a very simple climate model like the one used for that IPCC report and calibrated it to make sure it would yield the same results as the 1990 model. Then they fed in actual emissions data and added in the volcanic eruptions that have occurred, as well.

It sounds like they used a different, but similar model. Was there a reason they couldn't use the original one with updated parameters?

Surprise, surprise, reality tracks with scientific predictions. Although it's completely unremarkable considering it would be more surprising if the model turned out to be inaccurate, but still it is good news that it worked over such a long period of time.

Now if we could just convince someone in authority to do something about it. You know like someone who runs a country or something.

To really assess the IPCC projections, the researchers used a very simple climate model like the one used for that IPCC report and calibrated it to make sure it would yield the same results as the 1990 model. Then they fed in actual emissions data and added in the volcanic eruptions that have occurred, as well.

It sounds like they used a different, but similar model. Was there a reason they couldn't use the original one with updated parameters?

They write: "Fortunately, we can test this using a simple one-dimensional energy balance model (EBM) comparable to the main model used to make the 1990 prediction but following a popular simpler formulation."It appears to be one the authors have worked with in the past.

I have to admit, I've never heard of retroactively adjusting model estimates to match observation. Seems novel.

Not really. The original model assumed we'd put X amount of CO2 in the atmosphere and there'd be Y volcanic eruptions per year, etc. They re-ran the old model with the actual observed values for X and Y. So they didn't adjust the model itself, but rather the parameters. Turns out when they used observed values rather than the previous guesses, the model was an even better match than before, thus validating the model.

All they are doing testing the old model by adjusting some parameters. It seems to be a good model after all

I have to admit, I've never heard of retroactively adjusting model estimates to match observation. Seems novel.

If however one would like to improve modelling results going forward using better estimates of natural variability, that seems like a wonderful idea.

since the IPCC can't predict the future, they work from a number of more or less realistic emissions scenarios (which is why they should properly be referred to as "projections" rather than "predictions"). so they might have included a Pinatubo-scale eruption in 1995 rather than 1991, and global emissions of 35GT in 1999 rather than 28GT.

all these researchers have done here is re-run the models with the observed figures for GHG, aerosol, solar activity, etc. they're not adjusting to match observation.

the 1990 climate models were really quite simplistic, due to the limited computing resources of the day, so i'm not sure how much of this will be useful for improving the state-of-the-art. given that's it's amazing how good a job they were able to do...

There's some funny math/statistics in this article. How they can just retro-actively slap some variance statistics on some old prediction numbers, shift em around and say they are reasonable? That's stuff I did 5 years ago in my crappy labs, where our equipment sucked or we were just to lazy to do the experiment right, because we already knew the concepts trying to be reinforced by the lab anyway, so we just fudged the numbers.

The prediction model should have its own separate variance numbers from the measured values. If you wish to compare extrema, first correct each value separately, then compare the two. And certainly don't mix data types like using pre-corrected values for one set and then just giving the variance on another.

Going to read the full article now to see how fuzzy this is. EDIT- Nvm nature articles aren't free to read. EDIT2: Duh I should of just looked for the article elsewhere.

since the IPCC can't predict the future, they work from a number of more or less realistic emissions scenarios (which is why they should properly be referred to as "projections" rather than "predictions"). so they might have included a Pinatubo-scale eruption in 1995 rather than 1991, and global emissions of 35GT in 1999 rather than 28GT.

all these researchers have done here is re-run the models with the observed figures for GHG, aerosol, solar activity, etc. they're not adjusting to match observation.

the 1990 climate models were really quite simplistic, due to the limited computing resources of the day, so i'm not sure how much of this will be useful for improving the state-of-the-art. given that's it's amazing how good a job they were able to do...

I am not seeing where this write-up said that they re-ran the 1990 models using updated data. Am I missing something?

How about refuting the rest of the links? How about the pdf document as well where well over 1000 researchers refute the IPCC? I love how people just complain about one source then pretend they won the debate.

How about the pdf document as well where well over 1000 researchers refute the IPCC?

"Researchers"!!!!! Hoot!

31) 25 points– For every mail-in petition or other “list of names” showing AGW is wrong

I do love last season's Internet Performance Art, posed as new and fresh art!

The existence of the greenhouse effect was argued for by Joseph Fourier in 1824. The argument and the evidence was further strengthened by Claude Pouillet in 1827 and 1838, and reasoned from experimental observations by John Tyndall in 1859, and more fully quantified by Svante Arrhenius in 1896.

Now my question is how or why they overestimated the emissions. Clearly, the less emission the better

The collapse of the Soviet Union and its economy dramatically lowered emissions throughout the early 90's. I don't know if that is the only reason, but I know it was a huge factor in Russia's ability to meet their original Kyoto targets.

Now my question is how or why they overestimated the emissions. Clearly, the less emission the better

The collapse of the Soviet Union and its economy dramatically lowered emissions throughout the early 90's. I don't know if that is the only reason, but I know it was a huge factor in Russia's ability to meet their original Kyoto targets.

Yeah, until Heri Seldon is born, estimates of human emissions are not going to be scientifically predictable. Which is why they go into the "if this, then that" part of the modelling exercise, not the "therefore we predict X" part.

ROFLMAO c3headlines.com, that site is hilarious. You understand that 3 separate government investigations refuted every single detail on that page don't you? It is just wrong. You are just wrong. You have been wrong every time you've posted to Ars. In fact at this point its like "oh, its g0m3r619, that's wrong, moving on..."

How about refuting the rest of the links? How about the pdf document as well where well over 1000 researchers refute the IPCC? I love how people just complain about one source then pretend they won the debate.

How about the pdf document as well where well over 1000 researchers refute the IPCC?

"Researchers"!!!!! Hoot!

31) 25 points– For every mail-in petition or other “list of names” showing AGW is wrong

I do love last season's Internet Performance Art, posed as new and fresh art!

Best,

D

you need to learn how to debate. You didn't refute anything. All you did was essentially name call. Is this the best you can do?

Um, maybe you are not aware of it, but that is a link to a blog post collecting articles by already discredited individuals promoting theories that are also individually discredited.

Why would anyone waste time with the previously proven junk science Watts, McIntyre and others are promoting? If I want my 'science' on that level I'll go to Andrew Wakefield for medical advice while I'm at it...

I am not seeing where this write-up said that they re-ran the 1990 models using updated data. Am I missing something?

"To really assess the IPCC projections, the researchers used a very simple climate model like the one used for that IPCC report and calibrated it to make sure it would yield the same results as the 1990 model. Then they fed in actual emissions data and added in the volcanic eruptions that have occurred, as well."

so not technically the same model, but one that's extremely similar. as i noted above, the models they used for projections were incredibly simple (just trying to find a good description of what was actually included in the simulation), so you wouldn't expect much difference.

The most frequently cited projection estimates 0.7–1.5°C of warming between 1990 and 2030, which means we would see an increase of about 0.35 – 0.75 °C through 2010.

Is this actually correct though? As far as I understand, the temperature rise is not supposed to be linear, especially because of feedback effects...So wouldn't the 20 year temperature rise supposed to be slightly less than half the 40 year range?

Unless the 1990 IPCC report did not consider feedback effects, in which case, the next 20 years should see an increase greater than the last 20 years.

How about refuting the rest of the links? How about the pdf document as well where well over 1000 researchers refute the IPCC? I love how people just complain about one source then pretend they won the debate.

Did you even read the article? The onus lies on those 1000 researchers to now explain how the IPCC's predictions actually track with reality.